Containers that include a threaded closure member, such as bottles, jars or the like, typically include a smooth, integral thread formed on the neck portion of the container. When a closure having a corresponding thread is tightened on the container, there is a tendency for the closure to become loose. This loosening of the closure, commonly referred to as "backing-off", is due in part to vibration incurred during shipping and handling and to the self-lubricating properties of typically used plastic materials. In addition, these materials tend to flow or creep under stress, thus permitting the closure to work itself off to relieve the stresses set up in the threads due to tightening of the closure on the container.
Those skilled in the art will recognize that backing-off can be a significant problem to packagers in that containers having closures which are loose or appear to have been opened are less apt to be selected by consumers for fear of tampering and/or contamination.
Various closure designs have been used to solve the backing-off problem. One known container and closure includes spaced depending appendages extending from the lower edge margins of the threads on the container. The distal edges of the appendages form a second load-bearing surface which engages the threaded portion of an associated closure.
Another known design includes inwardly projecting tooth formations that engage tooth or ratchet formations located on the neck of the closure. Although this prevents inadvertent opening of the closure, this packaging design is typically for a single use application and has proven to be difficult, at best, to adapt to a multiple use application.
Another known design includes a two piece container closure having a lower portion which serves as a locking ring and can be provided with vertically depending auxiliary ridges that tend to bite into or engage an opposing surface in the container. The ridges hold the locking ring against rotation of the closure. One drawback to this design however is that the locking is provided in a separate piece from the actual closure itself.
It has also been observed that with conventional container closures, and particularly molded plastic closures, the lower edge of the cap must be provided with a type of recess to engage the lugged stripper bushing of a conventional "unscrewing" type of injection molding machinery to facilitate removal of the cap from the mold. In applications where the molded cap is used to enclose a container having locking formations on its neck threads, such recesses may interfere with the locking action of the closure on the container.
In addition, it has also been observed that in such lugged or toothed formations for preventing back-off, the closures, more frequently than expected, may not properly set on the container. That is, when "capping" the container, the closure may not engage the container, resulting in a "missed" package. This is problematic in that the capping apparatus must be stopped or shut-down and the closure and uncapped container removed or cleared from the apparatus.
Accordingly, there continues to be a need for a closure that provides significant back-off resistance to prevent loosening of the closure from the container after packaging. Such a closure further reduces the tendency for the closure to skew upon application to the container, and thus provides increased assurance that the closure properly seats on and engages the container during capping operations.